The three-dimensional structure of yeast phenylalanine transfer RNA is being studied by x-ray diffraction techniques. It is proposed to finish that work by collecting x-ray diffraction data to nearly 2A resolution. In addition, studies will be carried out on the mode of action of aminoacyl tRNA synthetases on tRNA. BIBLIOGRAPHIC REFERENCES: Three-dimensional Structure of Yeast Phenylalanine Transfer RNA at 3.0A Resolution, Nature, 248, 20-24 (1974) by F.L. Suddath, G.J. Quigley, A. McPherson, D. Sneden, J.J. Kim, S. H. Kim and Alexander Rich; Assay of Ester and Polyester Formation by the Ribosomal Peptidyl-transferase by Stephen Fahnestock, Helmut Neumann, and Alexander Rich, in Methods of Enzymology, Vol. 30, ed. by K. Moldave and L. Grossmann, Academic Press, New York, (1974), p. 489-497.